1. Field of the Invention
The present invention generally relates to a blue phase liquid crystal composition and a method for forming the blue phase liquid crystal composition. In particular, the present invention is directed to a blue phase liquid crystal composition with an induced blue phase property by properly blending a positive liquid crystal component and a negative liquid crystal component which both have no blue phase properties with respect to a certain chiral dopant. The chiral dopant is added to the liquid crystal blend to induce the blue phase property of the liquid crystal blend. A method is also disclosed for obtaining a blue phase liquid crystal composition with a blue phase property by properly blending a positive liquid crystal component and a negative liquid crystal component which have no blue phase properties with respect to a certain chiral dopant and by the addition of the chiral dopant.
2. Description of the Prior Art
A blue phase (BP) liquid crystal has a three dimensional photonic crystal structure. This liquid crystal phase usually exists between an isotropic phase and a cholesteric phase. A pile of molecular layers of the blue phase liquid crystal may form various stacking arrangements, such as blue phase 1 (BP1), blue phase 2 (BP2) or blue phase 3 (BP3) stacking arrangements such as body center cubic, simple cubic, and iso-like. Because light tends to have a shorter wavelength after Bragg diffraction in the molecular lattice, a bluish or purplish tone of mosaic texture can be generally observed, so the liquid crystal is named accordingly.
The most welcome feature of the blue phase liquid crystal material is the extreme short response time in the presence of an electric field. The liquid crystal display made of the blue phase liquid crystal material therefore has a super fast response, in the order of several hundred microseconds. Initially, the blue phase temperature range of the blue phase material was too narrow (around 1-2° C.) to be practicable, and this has continued to be the major applicable problem for the blue phase liquid crystal material. After years of study, however, it was found that the blue phase temperature range of the blue phase material may be enlarged to be in the order of tens of degrees (>60° C.) when blended reactive monomers of different ratios are photo-polymerized in the temperature range of the blue phase, theoretically temporarily solving the problem of a too-narrow blue phase temperature range of the blue phase material.
A liquid crystal display has a top polarizer and a bottom polarizer disposed in a way normal to each other (the axes are 90° to each other) so that no light is able to pass through. A blue phase liquid crystal material is able to change from a state of no birefringence to another state of birefringence, which is called the Kerr Effect. This is the reason why a blue phase liquid crystal material has a bright-dark (grayscale) appearance.
So far there are two major problems for the blue phase liquid crystal material. The blue phase temperature range of the blue phase material is still considered too narrow. Although certain blue phase liquid crystals of wide blue phase temperature range have been proposed, they are obtainable only by polymerization in an extremely narrow blue phase temperature range. It is difficult to precisely control the operations in such a narrow temperature range (within a few ° K) in the industrial field. Additionally, a very high drive voltage (more than 100 V) is needed, which is not beneficial for the design of the entire liquid crystal display hardware.
R. J. Miller and H. F. Gleeson (Liq. Cryst. 14, 2001 (1993)) have disclosed that six liquid crystals of blue phase property were obtained from six different liquid crystals with the addition of the same proportion of a chiral dopant. The resultant blue phase temperature range is 0.2° C. to 1° C., however, which is still too narrow.
In light of the fact that current formulation of the blue phase liquid crystals and the adjustments of the operating temperature were mainly based on empirical try-and-error methods, no universal principles exist to synthesize or formulate liquid crystals with blue phase property. The current solutions rely on trying every possible combination or wasting large quantities of materials for blending in search of a suitable formula. This approach costs a lot of time and money and decelerates the developments of the liquid crystal panel.
As a result, there is still a need to quickly formulate a blue phase liquid crystal composition of a wide temperature range with the liquid crystal materials of specific physical properties at hand or to obtain a liquid crystal composition of blue phase property from suitably blending a positive liquid crystal component and a negative liquid crystal component, wherein both components originally have no blue phase properties with respect to a certain chiral dopant and by the introduction of the chiral dopant.